This invention relates to a pressure sensor which permits an ultra fine element to be formed easily, and which is optimumly used to determine various kinds of pressures in the body, such as a blood pressure, etc. by incorporating the pressure sensor in a catheter and a guide wire inserted into the body, or by directly inserting the pressure sensor into a blood vessel and the like, and to form a photodetector type pressure sensor for a capillary and the like; and a method of manufacturing the same.
A pressure sensor of related art utilizing a photodetecting principle by using an optical fiber does not utilize an electric signal, such as a piezoresistive signal, etc. Accordingly, this pressure sensor rarely receives environmental disturbance ascribed to electricity and magnetism, and has a possibility of being applied to the interior of an organism (see Japanese Patent Publication No. 3128/1990, Japanese Patent Laid-Open No. 235731/1986 and Japanese Patent Laid-Open No. 201196/1996).
The pressure sensors using an optical fiber are roughly classified as pressure sensors of the type that have a cantilever beam type silicon structure fixed to a side surface of an optical fiber with a mirror, that face an end surface of the optical fiber, fixed to a front end of the beam, and that utilize the variation of the quantity of reflected light caused by the variation of the position of the mirror due to the flexure of the beam ascribed to pressure variation, and pressure sensors of the type that have on a front end of an optical fiber a silicon structure having a total reflection mirror serving also as a movable diaphragm, and joined to a glass structure and fixed to an end surface of the optical fiber by using a bonding agent, and that measure an amount of flexure of the diaphragm as variation of the intensity of the light.
However, in a pressure sensor of the type that utilizes a side surface of an optical fiber, a side wall is tapered to form a large etching window. This arrangement causes the dimensions of a pressure sensor portion to increase, and also makes it difficult to insert the pressure sensor into a working channel of a catheter and an endoscope, and obtain a pressure sensor capable of being inserted directly into a capillary, such as a blood vessel and the like.
There are related techniques including a method, as a method of fixing a total reflection mirror serving also as a movable diaphragm to a front end of an optical fiber, of forming a fine ring-shaped bonding agent layer on a posiresist layer, which is provided on a glass plate, by exposing the posiresist layer via an Al mask, transferring the bonding agent layer onto a front end of an optical fiber, fixing the resultant layer to a diaphragm formed and held in a frame of a silicon substrate via a holding portion, and cutting off the holding portion with a laser beam. However, in this method, the efficiency of transferring the bonding agent layer onto the front end of the optical fiber is low, and much time and labor is required to separate the diaphragm from the silicon substrate by cutting off the holding portion with a laser beam. Therefore, this method is inferior in the manufacturing efficiency of a pressure sensor and the yield thereof.
The present invention has been devised so as to eliminate the drawbacks, such as a low yield on the manufacturing of a pressure sensor portion, or a low yield on the connecting of a pressure sensor and an optical fiber together which are encountered in an optical fiber type pressure sensor of related art capable of being used in the interior of an organism such as a blood vessel, etc. and a capillary.
The present invention provides a pressure sensor wherein a reflective type movable diaphragm unit that has a mesa portion of a circular, thick SiO2 film, and a light reflecting mirror portion formed of a thin Al film in the center of a diaphragm portion formed of a circular, thin SiO2 film, and that has a ring-shaped spacer serving also as a bonding agent layer at a circumferential edge section of the diaphragm portion, is fixed in a sealed state to a front end, which has a half mirror layer thereon, of an optical fiber of not larger than 125 xcexcm in diameter, the diaphragm portion having a cross-sectionally substantially semicircular part.
The present invention further provides a method of manufacturing pressure sensors, the method including a step of accumulating SiO2 layers on a front surface of a silicon substrate and forming mesa portions by circularly leaving the SiO2 layers, a step of accumulating on a rear surface of the silicon substrate SiO2 layers as masks for separating reflective type movable diaphragms from the silicon substrate, a step of forming diaphragm portions by further accumulating SiO2 layers on the front surface of the silicon substrate, a step of forming light reflecting mirror portions by accumulating Al layers on the mesa portions, a step of forming around the diaphragm portions spacers serving also as adhesive layers and comprising polyimide, a step of separating the reflective type movable diaphragm units from the silicon substrate, a step of forming half mirror layers on front ends of optical fibers, a step of fixing the reflective type movable diaphragm units to the front ends of the optical fibers by inserting the reflective type movable diaphragm units into capillaries so that the end surfaces of the diaphragm units and those of the optical fibers are opposed to each other, bringing the reflective type movable diaphragm units and optical fibers into close contact with each other by microbeads and other optical fibers inserted from the other ends of the capillaries, and turning the polyimide layers into bonding agents by heating the diaphragm units, and a step of withdrawing the optical fibers from the capillaries, the step of forming the diaphragm portions including a step of accumulating SiO2 layers in annular grooves provided in the front surface of the silicon substrate and thereby forming cross-sectionally substantially semicircular parts.
The present invention still further provides a method of manufacturing pressure sensors, by forming a reflective type movable diaphragm unit and optical fibers by using the above-mentioned initial step to the step of forming half mirror layers; inserting the above-mentioned movable diaphragm units into capillaries so that the end surfaces of the diaphragm units and those of the optical fibers are opposed to each other; bringing the reflective type movable diaphragm units and optical fibers into close contact with each other by microbeads and other optical fibers inserted from the other ends of the capillaries; turning the polyimide layers into bonding agents by heating the diaphragm units, whereby the reflective type movable diaphragm units are fixed to the front ends of the optical fibers.